char * reverseOnlyLetters(char * s){

    int left = 0;
    int s_len = strlen(s);
    int right = s_len - 1;
    char temp;

    for (; left < right; left++, right--)
    {
        while(!islower(s[left]) && !isupper(s[left]))
        {
            left++;
            if(left >= right)
            {
                break;
            }
        }
        while(!islower(s[right]) && !isupper(s[right]))
        {
            right--;
            if(left >= right)
            {
                break;
            }
        }

        if(left >= right)
        {
            break;
        }

        temp = s[left];
        s[left] = s[right];
        s[right] = temp;
    }
    return s;
}